Inboard motorboat hull of the planing type having a cavitation plate



Jan. 3, 1956 s. P. OWEN 2,729,183

INBOARD MOTORBOAT HULL OF THE PLANING TYPE HAVING A CAVITATION PLATE Filed March 18, 1953 INVENTOR. SAMUEL PHILLIPS OWEN TTORNEYS INBOARD MOTORBOAT HULL OF THE PLANING.

My invention relates to an inboard motorboat. It has to do, more particularly, with the design and construction of the hull of a motorboat of the inboard motor and planing type. V

In ordinary small planing inboard motorboats, thebalance point is too far forward ,whenloaded with the crew ahead of the motor which is generally located just aft of an amidship position. This necessitates compromise designing to carry the load which results in poor planing performance, suction under the stern, and a generally bow-heavy performance, which, in some cases, becomes very dangerous.

It is the main object of my invention to provide a motorboat hull for an inboard motor planing type boat of such design that the center of buoyancy is shifted far enough aft in the boat to permit designing the boat with a straight keel with parallel bottom lines and with a light buoyant bow.

According to my invention I provide in the bottom of the boat at the stern two cut-outs or upward indentations which are open at their outer and rear sides. Between these two cut-outs, a narrow plane consisting of an extension of the dynamic support portion of the hull bottom continues on towards the stern and functions as an anti-cavitation area over the propeller and drive-shaft as well as to provide a convenient mounting location for the drive-shaft structure and the rudder. This arrangement has the effect of shifting the balance point of the supporting portion of the hull bottom, when at planing speed, back a distance equal to the fore-and-aft length of the cut-outs. Also, the weight of the hull over these cut-outs acts as an additional lever, when at planing speed, to move the balance point even farther aft.

The preferred embodiment of my invention is illustrated in the accompanying drawing wherein similar characters of reference designate corresponding parts and wherein:

Figure 1 is a side elevational view of an inboard motorboat constructed according to my invention.

Figure 2 is a bottom plan view of the boat of Figure 1.

Figure 3 is a stern view of the boat of Figures 1 and 2.

Figure 4 is a stern view illustrating a modification of the cut-outs at the stern.

Figure 5 is a view similar to Figure 4 and illustrating another modification of the cut-outs.

Figure 6 is a side elevational view of the stern portion of a boat illustrating a different arrangement for the cavitation plate, integral with the hull, and illustrating the associated rudder.

With reference to the drawing, Figures 1, 2 and 3 illustrate one form of my invention. The hull 10, to achieve maximum performance, is designed with a straight keel and parallel bottom lines. The motor 11 is disposed in the usual location centered relative to the keel line and slightly aft of an amidship position. The motor 11 directly drives the propeller 12 in the usual way by the driveshaft 13.

According to my invention I provide at the stern, the

2,729,183 Fatented Jan. 3, 1956 outer sides at the outer sides of the boat. They are so arranged that they provide a narrow plane between them which acts as a cavitation plate 15 over the propeller 12 and shaft 13. The cut-outs 14 are shown in Figures 2 and 3 as each having a flat top wall 16, a forward wall 17 perpendicular thereto, and an inner wall 18 perpendicular to the top wall 16 and at right angles to the forward wall 17. However, the cut-outs '14 need not be of this particular shape. For example, in Figure 4, I have shown cutouts 14a, in which the inner side walls 18a curve and merge with the top wall 16a. In Figure 5., I have shown sharp angle relative to the bottom of the boat.

The narrow extension of the dynamic support portion of the boat bottom, forming the cavitation plate. 15, may

extend frornthe front of the cut-outs tothestern as shown in Figure 1 or, as shown in Figure 6, the integral cavitation plate'l5a may terminate short of the stern. With the arrangement of Figure l, the rudder 19 is supported by andbelow the rear end of the cavitation plate 15 while with the arrangement of Figure 6 the rudder 19a is'sup-" ported independently of the cavitation plate 15a and directly behind it.

It will be apparent that the two cut-outs 14, 14a or 14b on the bottom of the boat begin at the stern and run forwardly a distance which is variable and depends on the length of the boat and its point of balance. Usually, this will be approximately 7% to 11% of total boat length. Heights of the cut-outs will vary according to boat length, draft and buoyancy desired when the boat is at rest in the water. The upper solid line in Figure 1 shows the water line when the boat is at rest. The narrow cavitation plate or strip extends from the front of the cut-outs to the stern, as shown at 15 in Figure 1, or, if desired, a partial distance from the front of the cut-outs to the stern, as shown at 15a in Figure 6. This strip, which is an integral part of the hull can be of variable width as required to prevent air from interfering with the effectiveness of the propeller or rudder.

These cut-outs are not steps in the accepted sense of hydroplane terminology inasmuch as the trailing edges of the cut-outs do not offer any dynamic lift while the boat is under way. Instead, the entire area of these cut-outs becomes completely free of water contact once the boat reaches a reasonable planing speed, indicated by the lower dotted line in Figure 1, since the boat has a forward motion faster than the depressed area of water under the hull and can again rise to a level with the body of water surrounding the boat.

The purpose of my hull design is twofold:

1. To establish a center of buoyancy in relation to the planing portion of the hull (that which supports dynamic lift) further aft than is now possible with direct drive of engine to propeller and of conventional monoplane design. In'relation to the entire length of the boat, the center of buoyancy in planing attitude will move back a distance somewhat greater than the fore-and-aft length of the cut-outs due to the weight of that part of the hull and its contents above the cut-outs. This weight acts as leverage to further move the planing balance point aft. With this new balance point, the forward portion of the hull will become lighter, creating a safer craft and also one that can absorb cleaner and swifter bottom lines than is now possible.

2. The cut-outs also eliminate static buoyancy, allowing the back portion of the hull to rest lower in the water and, consequently tend to allow the forward portion of the hull to fioat somewhat higher, thereby causing the craft to rest with the keel more parallel with the water line of the craft. This improved attitude, when at rest, allows the craft to raise to a planing position with a lower overall. bow, raise than .with, conventional. bulls and conse-- quently. minimizes thechanges in. attitude. between at rest position in the water .and atplaning speed positionin the water.

In summary, planing craft properly utilizing my hull arrangement will be faster than conventional monoplane motor boats, will be safer due to a lightenedcbow, and will, have a more moderatechange in attitude allowing greater .visibility in allaround performance.

7 ,Various other advantages will beapparent. v

v'I-Iavingthus.described my invention, what I claim is: ,1. A. motorboat'of the inboard motor. and planing type comprising a-hull having a pair of identical cut-outsin thcbottom at its stern witha. cavitation-plate therebetween extending amidship'from a line coinciding with the forward walls of said cut-outs towardsthestern of the boat, said cavitation'plate having alower surface which is .a continuation of the surface of thebottom-of .the hull, said cut-outs being open at their outer and rear sides and the forward wall of each cut-out being at an-abrnpt angle relative to the bottom surface of the hull, the stern ofithe cavitation plate also terminating .at-anabrupt angle relative to the lower surface thereof, and ,apropeller driven from the motor of the boat and located beneath said cavitation plate.

2. A motorboat according to claim 1 wherein the cavitation plate is an integral part of the hull.

3. A motorboat according to claim 1 wherein the cavitation plate terminates at the stern of the boat.

4. A motorboat according to claim 1 wherein the cavitation plate terminates at a point spaced ahead of the stern of the boat.

5. A motorboat according to claim 1 wherein the inner walls of the cut-outs merge with the cavitation plate.

6. A motorboat according to claim 1 wherein the inner walls of the cut-outs are at an abrupt angle relative to the cavitation plate.

7. A motorboataccording to claim 1 wherein the inner walls of the cut-outs are angularly disposed relative to the cavitation plate.

References Cited in the file of this patent UNITED. STATES PATENTS 1,352,753 King Sept. 14, 1920 1,755,709 Small Apr. 22, 1930 1,805,131 Donaldson May 12, 1931 2,519,793 Rowe Aug. 22, 1950 FOREIGN PATENTS 84,357 France Feb. 9, 1869 

